In general, when a cutting process is carried out, heat is generated by: (1) shearing deformation of a material to be cut, (2) friction on a cutting face, (3) friction on a flank, and so on. As a result, wear of a tool may be thermally generated, and/or surface quality of a material to be cut may be adversely affected.
On the other hand, when a temperature of the material to be cut is increased, cutting resistance is reduced, which is of benefit. In addition, built-up edge is also reduced, which is of benefit.
Therefore, in order to carry out a cutting process in an optimal way, it is important to recognize a temperature of a tool when the cutting process is carried out.
In particular, in recent years, in a technical field of ultra-precision cutting process, a tool made of single crystal diamond is used. However, the heat resistance of a tool made of single crystal diamond is about 600° C. at the highest. Therefore, it is necessary to monitor a temperature of the tool during a cutting process.
In addition, when a cutting process is carried out for a material such as a resin whose melting point is low, for example urethane, the cutting temperature has to be controlled within a proper low-temperature range (100° C. to 200° C.). However, if a cutting speed is restrained so as to restrain the cutting temperature, adhesion and/or built-up edge may be generated.
Therefore, when a tool made of single crystal diamond is used, and/or when a cutting process is carried out for a material such as a resin, it is important to recognize a temperature of a tool when the cutting process is carried out, in order to optimize conditions for the cutting process.
In order to recognize a temperature of a tool when the cutting process is carried out, conventionally, there is used (1) a method using a radiation thermometer, or (2) a method using the tool and the material to be cut as a thermocouple. For example, JP 2006-102864 A1 discloses a cutting test machine adopting the method (2).
FIG. 6 shows principle of temperature measurement according to the method (2). As seen from FIG. 6, a tool 52 and a material to be cut 53 form a thermocouple, so that a temperature of the tool 52 during the cutting process can be measured. Specifically, in the apparatus for a cutting process 50, the material to be cut 53 is connected to a voltage measuring unit 65 via a chuck 51, a mercury layer 54 and a lead wire 61. On the other hand, the tool 52 is also connected to the voltage measuring unit 65 via another lead wire 62. Accordingly, thermal electromotive force therebetween can be measured.